VM crash: regexp_assembler_ir.cc: 329: error: unreachable code

[alexmarkov]

Seen 1 flaky VM crash on vm-kernel-win-product-x64 bot

  FAILED: dartk-vm product_x64 corelib_2/double_hash_code_test
  Expected: Pass
  Actual: Crash
  --- Command "vm" (took 01.000109s):
  set DART_CONFIGURATION=ProductX64 & set DART_SUPPRESS_WER=1 & set DART_CRASHPAD_HANDLER=C:\b\s\w\ir\out\ProductX64\crashpad_handler.exe & out\ProductX64\dart.exe --no_intrinsify --ignore-unrecognized-flags --packages=C:\b\s\w\ir\.packages C:\b\s\w\ir\tests\corelib_2\double_hash_code_test.dart
  exit code:
  1073741845
  stderr:
  isolate terminated by vm
  c:\b\s\w\ir\cache\builder\sdk\runtime\vm\regexp_assembler_ir.cc: 329: error: unreachable code
  --- Re-run this test:
  python tools/test.py -n dartk-win-product-x64 corelib_2/double_hash_code_test

full log

It looks like regexp code does not handle unwind exceptions properly.
Created the following test to reproduce the crash reliably:

// VMOptions=--intrinsify
// VMOptions=--no_intrinsify

import "dart:isolate";
import "dart:async";
import "package:expect/expect.dart";

isomain1(replyPort) {
  final regexp = new RegExp('[ab]c');
  while(true) {
    Expect.equals(4, regexp.allMatches("acbcacbc").length);
  }
}

void main() {
  for (int i = 0; i < 20; ++i) {
    ReceivePort reply = new ReceivePort();
    Isolate.spawn(isomain1, reply.sendPort).then((Isolate isolate) {
      new Timer(new Duration(milliseconds: 50), () {
        print('killing isolate $i');
        isolate.kill(priority: Isolate.immediate);
      });
    });
    reply.close();
  }
}